The invention relates to a method for preventing an uncontrolled rollback of a vehicle with released brake by influencing the toque transmission through the drive train between a motor and at least one driven wheel as well as vehicle equipped accordingly. For example, influencing the torque transmission is accomplished by controlling engagement of at least one clutch or its actuators. In case a rollback status is determined, i.e. a movement in opposite direction as the predetermined direction of the motor vehicle is determined, a means for influencing the torque transmission, i.e. for example the clutch, is controlled such that the drive train creates a torque that acts against the rollback movement.
Various methods are known attempting by means of superimposing a torque to reduce rollback to zero, i.e. a movement of the vehicle with released brake in the direction opposite to the desired direction. For instance, in typical automatic transmissions the torque converter transmits a drive torque when a drive forward mode is chosen. This torque can be chosen such that the motor vehicle at any incline can hold the vehicle in place even without using the brake or increasing the rotational speed of the motor. Frequently, these properties are perceived as very comfortable. Therefore, suggestions are known preventing a rollback at a variety of possible inclines. In this connection, it is for instance pointed to DE 10239392A1, DE 102004017635A1 and DE 19910573A1. The latter discloses for example the possibility to prevent rollback of a vehicle having a dual clutch transmission. It has been found that the goal that is to be accomplished, namely zero movement of the vehicle, cannot or hardly can be achieved due to measurement tolerances of the speed sensors as well as a lack of ability to determine all drive parameters, as the present incline of the road, and in addition the inconsistent results in the driving reactions makes the driver insecure.
All suggestions as described above have in common that a possible rollback can be prevented entirely. However, under some driving conditions occurring in practical use, a rollback might be desirable, for example a driving maneuver without complicated and time consuming change of the transmission mode.
From the DE 198 49 494 C1 it is known in an almost standstill state of a vehicle to allow a rolling speed in opposite direction to the desired driving direction wherein the rolling speed is limited to a predetermined speed. The limit is accomplished by the predetermined speed by means of braking, influencing the motor speed and/or influencing the torque transmission through the drive train. According to the teaching according to DE 198 49 494 C1 zero movement of the vehicle is prevented for giving the driver the perception of the actual road parameters and to urge the driver to take additional measures preventing the continued movement opposite to the desired driving direction, as for example actuating the brake. By controlling the rolling speed to a definite speed even in case of strongly inclined roads a high load results for the vehicle systems, in particular for the systems involved in the transmission of torque, such as torque converter or clutches. Even though this problem has been addressed in DE 198 49 494 C1, as a solution, limiting the rolling distance has been suggested by braking the vehicle and urging the driver to a new start. This can be very irritating for the driver since he might perceive this as depriving him of the control over the vehicle and can result in incorrect reactions by the surprised driver. Further, the driver will probably not get a chance to get used to this since such automatic action will only occur very infrequently.